Microfilm readers are now available that both optically display the information contained in a frame of microfilm and also electronically scan the same image. The electronically scanned information may be used on a network to provide a remote image on a display or the information may be stored or used to make a hard copy of the image using some type of a printer. Because the image resolution required for the scanned image is high, a scanner, typically a linear sensor array is used to convert the image line by line, into an electrical output. During the scanning operation, the optically displayed image is usually blanked. Reference is made to U.S. Pat. No. RE 32,137, which describes a method to scan microfilm using a linear sensor.
Accurate reproduction of a scanned image requires that the image be optimal during scanning. Optimzation may include such functions as exposure control, focus, as well as image positioning. Currently, this requires several scans with the linear sensor to provide the required optimization. The time required for pre-scanning each image reduces productivity so in an effort to speed the printing operation the operator assumes that all the images in a group, share common exposure characteristics requiring only one pre-scan for the entire group; such a practice can compromise the quality of some of the images.
Microfilm retrieval stations of this type have the optically projected image appear on a rear projection screen. The optical path for the electronically scanned image will be separate and distinct from the viewing path. As a result, alignment of the two paths is difficult, and any error in such alignment will result in slightly different images being projected along each path. Thus, in the event one wanted to enlarge or zoom in on a portion of the image and then scan that same section, the misalignment that may exist could be intolerable.
Another problem with a rear projection viewing screen is that it is difficult to provide sufficient light to make the screen image bright enough and still maintain a pleasing contrast ratio for viewing in a normal office environment. Moreover, as the level of illumination on the screen approaches a satisfactory level of brightness, there may be more illumination than required for the linear scanning array.
After viewing an optically formed image on a screen, an operator may desire to scan just a Portion of that image. Present microfilm retrieval station require either the use of an optical mask or inputting the coordinates of the desired portions of the image to be scanned. Such procedures are not very productive because of the ungainly and complicated steps that must be performed by the operator.